package org.apache.lucene.util;

import java.util.concurrent.atomic.AtomicLong;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * Simple counter class
 * 
 * @lucene.internal
 * @lucene.experimental
 */
public abstract class Counter {

    /**
     * Adds the given delta to the counters current value
     * 
     * @param delta
     *          the delta to add
     * @return the counters updated value
     */
    public abstract long addAndGet(long delta);

    /**
     * Returns the counters current value
     * 
     * @return the counters current value
     */
    public abstract long get();

    /**
     * Returns a new counter. The returned counter is not thread-safe.
     */
    public static Counter newCounter() {
        return newCounter(false);
    }

    /**
     * Returns a new counter.
     * 
     * @param threadSafe
     *          <code>true</code> if the returned counter can be used by multiple
     *          threads concurrently.
     * @return a new counter.
     */
    public static Counter newCounter(boolean threadSafe) {
        return threadSafe ? new AtomicCounter() : new SerialCounter();
    }

    private final static class SerialCounter extends Counter {
        private long count = 0;

        @Override
        public long addAndGet(long delta) {
            return count += delta;
        }

        @Override
        public long get() {
            return count;
        };
    }

    private final static class AtomicCounter extends Counter {
        private final AtomicLong count = new AtomicLong();

        @Override
        public long addAndGet(long delta) {
            return count.addAndGet(delta);
        }

        @Override
        public long get() {
            return count.get();
        }

    }
}
